1. Field of the Invention
The present invention relates to a thermal printer having a line thermal head, particularly to a thermal printer using a tag provided at one side edge thereof (hereinafter referred to as a tag).
2. Prior Art
FIGS. 21 and 22 show a conventional typical thermal printer capable of performing printing on a tag.
The thermal printer comprises a supporting shaft 1, a collar 2 in which the supporting shaft 1 is slidably rotatably engaged, an innermost roll presser plate 3, a roll holder 4 and a boss 5 which are respectively fixed to central inner and outer surfaces of the innermost roll presser plate 3 wherein central holes of the innermost roll presser plate 3, roll holder 4 and boss 5 are respectively engaged in the collar 2 and the boss 5 is fixed to the collar 2 by way of a screw 6, whereby the innermost roll presser 3 is positioned relative to the collar 2 in the axial direction thereof, i.e., left and right directions in FIG. 21.
A tag roll 7, which is formed by winding a tag 10 around a core 8 in a roll shape, is engaged in the roll holder 4 as illustrated in FIG. 22 and a front side roll presser plate 11 is fixed to the collar 2 by inserting the collar 2 into a hole 11a defined at the central portion thereof.
The tag is a type for use in price tags, etc. and has a plurality of threads 9 at one side thereof (hereinafter referred to as threads 9) wherein when it is set on the tag roll, an entire tag roll 7 is pressed by the front side roll presser plate 11 by way of the threads 9 whereby the rear surface 7a of the tag roll 7 is pressed against the innermost roll presser 3. At this state, the front side roll presser plate 11 is fixed to the collar 2 by screwing a screw 13 into a boss 12 which is integrated with the front side roll presser plate 11.
Accordingly, the tag roll 7 is turned relative to the supporting shaft 1 together with the roll holder 4, the collar 2, etc. at the state where it is held between the innermost and front side roll presser plates 3 and 11 without unwinding the tag 10.
The tag 10 wound around the tag roll 7 is successively drawn out from one end thereof, as illustrated in FIG. 22, and is conveyed in the direction of the arrow A while it is held by a thermal head 21 and a platen 22.
In the course of conveyance of the tag 10, the tag 10 is guided along a tag guide roller 14 toward the direction of the arrow A and the threads 9 are swept away from a printing surface 10a (hereinafter referred to as a printing surface 10a) by a thread sweeping brush 15 so that the threads 9 hang down outside the tag 10.
When the hanging threads 9 reach tag guides 17 and 18 capable of positioning the tag in the width direction thereof, the threads 9 get on the corner of the printing surface 10a. At this state, a given printing is performed on the printing surface 10a at the printing portion while the tag 10 is held by the thermal head 21 and the platen 22 by way of an ink ribbon 19.
The tag guide 17 is fixed while the tag guide 18 is movable and adjustable in the width direction of the tag 10.
However, according to the conventional thermal printer, even if the threads are swept away from the printing surface by the thread sweeping brush, the same threads get on the printing surface again when the tag is guided by the tag guide, which restricts the width direction of the tag, at the both side edges thereof. As a result, the threads are liable to pass through the thermal head and platen at the time of printing, which leads to the deterioration of the printing quality.
Inasmuch as the thread sweeping brush is disposed only at the position adjacent to a tag roll holding device comprising two roll presser plates, etc., if the thread is a type such as a silk thread having a property to jump up, such thread is liable to get on the printing surface before it reaches the thermal head and the platen even if it is swept away by the thread sweeping brush, which causes deterioration of the printing quality when it gets on the printing surface before it reaches the printing position.
Furthermore, since the conventional thermal printer has a structure to hold both side edges of the tag to be conveyed by a pair of tag guides to thereby restrict the width direction of the tag, if the interval between a pair of tag guides is tightly set, the tag and the thread are liable to be damaged due to the strong pressing of both side edges of the tag by a pair of tag guides. If the interval between a pair of tag guides is loosely set, the tag is conveyed while it is positioned on either side of the tag guide, which causes the displacement of the printing position relative to the tag.
Inasmuch as the thread which gets on the printing surface as it is successively drawn out from the tag roll is intended to be swept away from the printing surface by the thread sweeping brush after it passes through the tag guide roller, such thread is liable to become entangled with another thread when the thread is pressed against the printing surface at the time of passing through the tag guide roller or liable to be caught by notches which are formed at equal intervals along both side edges of the tag in the conveying direction thereof, whereby poor conveyance or deterioration of the printing quality may result.
In case of the tag roll holding device which is provided in the conventional thermal printer as illustrated in FIG. 21, when the front side roll presser plate 11 alone is removed and the core 8 of the tag roll 7 is engaged in the roll holder 4 integrated with the innermost roll presser plate 3 which is attached to the body of the tag roll holding device and thereafter the front side roll presser plate 11 is pressed against and fixed to the tag roll 7, the threads 9 on the tag roll 7 positioned immediately above the core 8 get over the core 8 and hang down while the threads 9 on the tag roll 7 positioned under the core 8 hang down so that the threads 9 are positioned under the outer periphery of the tag roll 7 at the distal ends thereof.
Accordingly, when the front side roll presser plate 11 is pressed against and fixed to the tag roll 7 at that state, the threads 9 are crushed so that the thread 9 or the thread 9 and tag 10 are liable to be entangled with one another, whereby the entangled threads or the entangled thread and tag are liable to be caught by the tag roll when the tag is successively drawn from the tag roll, which causes obstacles to the thermal printer.
To solve these problems, it is necessary to set the threads between the innermost and front side presser plates at the state where the threads are lined up to prevent the threads from being entangled with one another or being caught by the notches when the tag is drawn out from the tag roll at the time of setting the tag, which leads to the troublesome handling.